Studies of Thyrotropin-Releasing Hormone (TRH) are being conducted at several levels of biologic organization: intact man, the intact rat, the in vitro rat adenohypophysis. Utilizing a specific and sensitive TRH radioimmunoassay and affinity chromatography, TRH secretory physiology will be examined systematically by quantitation of TRH in peripheral blood in both man and the rat. Emphasis will be placed upon the most relevant variables; core temperature, thyroidal status, diurnal cyclicity, and glucocorticoid influences. Corroboration of TRH identity in tissues, such as that found in hypothalamus and pineal, will be obtained by immunoassay, in vitro bioassay with isolated pituitaries, chromatographic behavior in one dimensional thin layer systems, and degradation kinetics in serum, in comparison to synthetic TRH standards.